A. Field of the Invention
This invention relates to accessories for use with visual display devices of the type used with video display terminals (VDT's), lap-top computers, television sets, and the like. More particularly, the invention relates to a visor for reducing the amount of ambient light impinging on the viewing screen of a VDT display device, or similar display device.
B. Description of Background Art
Video display terminals (VDT's) are used in great numbers to display electronically processed information. Displayed information can include alpha-numeric characters as well as graphical images. Display devices used in VDT's include cathode ray tubes (CRT's), liquid crystal panels and gas discharge devices.
Video display terminals, many of which employ CRT's, are being utilized by an increasing number of people. Large numbers of VDT's are used in business, security, military operations, scientific or academic work, computer-aided design, or pleasure games and hobbies, to name just a few applications employing VDT's.
A substantial percentage of VDT users are required to spend a large portion of their work day viewing information displayed on the CRT screen of a VDT. Not surprisingly, frequent users of VDT's have found that prolonged viewing of a CRT screen can cause eye strain, and physical and mental fatigue. In a report titled "Symptoms in Video Display Terminal Errors in the Presence of Small Refractive Errors" and published in September, 1988 in the Journal of the American Optometric Association, it was stated that 60 to 81% of those using a VDT for 6 hours or more per day reported experiencing significant eye strain and/or headaches. Aside from the fact that such negative effects of prolonged viewing of a VDT are unpleasant for those who must spend a substantial portion of their time at a computer terminal, resulting eye strain and fatigue can adversely affect job performance, by increasing the likelihood of operator errors or omissions.
A number of factors contribute to operator eye strain which can be caused by prolonged viewing of VDT's. For example, if the ambient light on the CRT face plate is too intense, the brightness of illuminated graphics displayed on the CRT phosphor screen relative to unilluminated areas, i.e., the contrast ratio, is reduced. With a reduced contrast ratio, the eye must strain to perceive the displayed image, causing discomfort if the operator is required to view such low-contrast ratio images over a prolonged period.
In addition to viewing difficulties caused by reduced contrast ratios resulting from certain conditions of ambient light that illuminates a CRT face plate, specular reflections of light off of the glass CRT face plate can sometimes glare directly into the eyes of the operator, further reducing visibility of images on the CRT screen, and further increasing the discomfort of the operator.
Another undesirable visual effect often encountered when viewing small characters or other images on a CRT screen is the appearance of a "halo" surrounding the illuminated picture elements (pixels). The halo can decrease the "sharpness" or resolution of the illuminated image. Also, halos can appear to overlie adjacent pixels, reducing their visibility.
From the description above, it is evident that a need exists for improving the viewability of images displayed on a CRT or other VDT display device to reduce eye strain, and increase display resolution, thereby increasing the comfort and efficiency of those who must use the VDT for prolonged periods. In response to this need, a variety of types of filters have been proposed for use with VDT's.
In U.S. Pat. No. 4,989,953, Feb. 5, 1991, Kirschner, Video Display Terminal Filter, the present inventor disclosed a novel and highly effective VDT filter, for improving the contrast and viewability of displays. That filter utilizes a thin transparent sheet of a soft polymeric material such as polyvinylchloride, which is adhered directly to the face plate of a VDT with the aid of a thin film of water applied to the face plate. Filters disclosed included those dyed with neutral gray for use with black and white or color CRT's (red, green, blue). A particularly novel development disclosed in the referenced patent is the inventor's discovery that filters of the type described which were dyed with a color subtractively complementary to the peak emission color of the display device provides a dramatic increase in contrast. Thus, a magenta-colored filter was found to be highly effective for use with CRT's employing a green phosphor screen. A bluish-colored filter proved highly effective for use with amber-colored displays.
When the face plate of a CRT or other VDT display device is illuminated with sufficiently high levels of ambient light, glare and contrast reduction can decrease viewability to an uncomfortable level, even if the VDT is provided with a highly effective colored filter of the type described above. In those situations where the sources of ambient light cannot be controlled directly, some sort of shield must be placed between a light source and a VDT, or the VDT must be re-positioned, to reduce the amount of light impinging on the VDT face plate to an acceptable level. The following U.S. patents disclose devices intended to reduce the level of ambient illumination of the face plate of a CRT or other display device.
Hursey, U.S. Pat. No. 3,961,159, Jun. 1, 1976, Light Shield/Support Device; Giulie, et al., U.S. Pat. No. 4,444,465, Apr. 24, 1984, CRT Shield; Kopich, U.S. Pat. No. 4,569,572, Feb. 11, 1986, Hood For Video Terminals: Giulie, U.S. Pat. No. 4,633,324, Dec. 30, 1986, CRT Shield: Tierney, U.S. Pat. No. 4,784,468, Nov. 15, 1988, Display Monitor Shield Assembly; PA1 Gart, et al., U.S. Pat. No. 4,788,597, Removable Conforming Video Display Terminal Filter.
The present invention was conceived to provide an improved ambient light shielding device adapted for use with VDT's of a variety of shapes and sizes. A further goal of the present invention was to provide means to discourage unauthorized viewing of data on a VDT screen. With the proliferation of lap-top computers used in airplanes and other public places, it would be desirable to provide an accessory which hinders viewing of confidential or sensitive data displayed on a VDT screen, by an adjacent passenger or other member of the public.